1. Field of the Invention
The present invention relates to a wind turbine system, an assembling method, an inspecting method, and an operation method of a wind turbine system and especially to a connecting way between a hub and a main shaft.
2. Background Art
A wind turbine system has been introduced broadly as a main tool among renewable energy sources. In the wind turbine system, rotating energy is transmitted to the main shaft via rotation of the hub which supports blades, and a generator is also rotated by the rotation of the main shaft. Thus, electricity is generated in the generator.
In U.S. Pat. No. 4,757,211, an example of a conventional wind turbine system is shown. In this literature, the following components are disposed in a nacelle, that is, a hub which supports blades and rotates with the blades, a main shaft connected to the hub and disposed in the inner diameter side of the hub, a gear box connected to the main shaft, and a generator which receives the rotating energy via the gear box and the rotating speed becomes higher through the gear box.
In the wind turbine system described in the U.S. Pat. No. 4,757,211, the main shaft is connected to the hub at an outside portion of the hub, therefore the main shaft length in the axial direction becomes longer. If the main shaft length in the direction becomes longer, torsion is generated in the rotating direction when rotating the blades and the hub. The torsion can give rise to a reduction of transmission efficiency of rotating power, or a damage to the main shaft by being added of excess load to the main shaft. That is, reducing the efficiency of generating electricity or shortening the lifetime of the wind turbine system can be occurred.